W.Y.LEONG1, I.Y. GOON2, S.H. CHOTIRMALL1, P. SONG2, A. GUPTA2, M. LOH1, J.C. CHAMBERS1
Nanyang Technological University1, Imperial College London, London, UK2
The use of inappropriate reference equations affects the accuracy in interpretation of spirometry testing and often lead to erroneous estimation and mis-diagnosis. There is currently an absence of a standardized spirometry reference values for South Asians. Hence, we aim to derive new predictive equations that are specific for this population and evaluate their performance against other published reference values.
The Global Health Research Unit (GHRU) study is a population cohort from Bangladesh, India, Pakistan and Sri Lanka. Baseline spirometry measurements were obtained from 7453 subjects (5477 females, 1976 males) >=18 years; which were randomized into training (n=5589) and test (n=1864) dataset. We developed three predictive equations for forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1), and FEV1/FVC ratio using linear regression with age, height, weight and countries as covariates in training data and validate them using the test data.
Except for model 1 (covariates: age and height) in men, predictive accuracy were on average within 2% of observed (range= 99.7%-101.2%), in both men and women. Large fraction of subjects in a healthy population were classified as “abnormal” when using other published reference values, compared to <10% in our predictive equations. Similar observations were noted when applied to an external dataset of South Asian descents in Singapore.
Our current predictive equations performed favourable to other published reference values for South Asians. This will provide a standardize equation for spirometry users and help improve accuracy in diagnosis of lung function; even for South Asian descents from other geographical location.